Explosive devices such as improvised explosive devices (IED) and land mines pose a threat to armoured land vehicles. Such explosive devices are typically placed on the ground, just above ground level or can be buried. Encountering of an explosive device by a land vehicle can trigger the device to explode under the vehicle and thus an under-vehicle blast. Such a blast can cause injuries or death of passengers of the vehicle and damage to the vehicle and cargo. This is not only because the floor of the vehicle can break, so that hot gasses, debris, shrapnel and floor fragments can enter the cabin, but also because of the impact due to the blast. The sudden acceleration of the vehicle can cause a shock to a passenger, which can cause brain injuries, spine injuries and other visible and invisible trauma. The vehicle may also roll-over due to a blast. The risk thereof increases with a higher centre of gravity of the vehicle.
In recent conflicts, IEDs are more frequently deployed and have increased explosive strength. Protective measures for armoured vehicles against under-vehicle blasts have therefore become more important. However, at the same time, high manoeuvrability and reduced weight are important requirements for armoured vehicles, for example to allow their use in urban environments. For these reasons, a need exists for protective measures for vehicles against blasts which allow a vehicle to remain relatively light-weight and highly manoeuvrable.
Traditionally, armoured vehicles are provided with a flat floor. Stiff structures are used to carry loads from blasts from under-vehicle mines. The stand-off of the vehicle (distance between ground-level and vehicle bottom) is kept as large as possible. The blast pressure is received by the vehicle bottom, resulting in deformations, which are desired to be limited. Recently, V-shaped hulls have been used for improved protection against IEDs. For example, Stryker vehicles have been manufactured and retrofitted with a V-hull for improved performance against IEDs compared to the traditional flat-bottom configuration. The downward pointing V-shaped geometry is intended to deflect upward propagating blasts occurring under the vehicle. An exemplary V-shaped (or diamond-shaped) hull design is disclosed in US-A-2007/0 186 762. A disadvantage of V-shaped hulls is that a vehicle provided with such a hull generally has a higher centre of gravity of the vehicle, which increases the risk of roll-over of the vehicle.
U.S. Pat. No. 8,365,649 relates to a composite armour assembly having a convex downward-facing centre surface and concave downward-facing sides, in particular FIGS. 1A and 4E. The major convex centre part results in worse pulse transfer and limited or no membrane forces under blast loading. US-A-2011/0 088 544, FIG. 3, relates to an armour plate with side walls in the form of concave chutes, and a broad flat plate in the centre. WO-A-2008/127272 relates to a stepped V-shaped bottom hull for an armoured vehicle, in particular FIGS. 1B and 2.
US-A-2012/0 247 315 describes a blast-protection element for a land vehicle having an exterior impact surface defining a cross-sectional profile defining a smooth continuous curve, wherein the exterior impact surface is convex. The blast-protection element is, when in use attached to the vehicle, oriented convexly relative to the ground plane. A disadvantage of such a blast-protection element is that it is almost horizontal next to its centreline. Blasts occurring near the centreline are thus not efficiently deflected sideward.
US-A-2007/0 084 337 describes a vehicle under-structure comprising an inwardly bent downwardly concave armoured bottom plate mounted on a bottom of a vehicle, the bottom plate being formed with at least one bending edge extending longitudinally with respect to the vehicle.
US-A-2003/0 010 189 describes a concave, homogenous protective floor plate having a large radius for an armoured vehicle.
US-A-2011/0 314 999 disclosed a curved underbelly device for an armoured vehicle including curvilinear, saddle and sinusoidal shapes.
Gurumurthy, “Blast mitigation strategies for vehicles using shape optimization methods”, master thesis MIT, September 2008, http://hdl.handle.net/1721.1/45759, describes the 2D modelling of the flow of a blast wave around a vehicle with a vehicle hull, including a concave hull, simulated as a non-deformable solid object and having a half consisting of a quarter circle. It was observed that a V-shape showed the best performance over all blast intensity levels in terms of minimising the peak head-on impulse.
BIPS 06/FEMA 426: Reference Manual to Mitigate Potential Terrorist Attacks against Buildings, 2nd Edition, October 2011, describes that when an incident pressure wave impinges on a structure that is not parallel to the direction of the wave's travel, it is reflected and reinforced. This results in the structure being exposed to a reflected pressure that is greater than the incident pressure (or side-on pressure). The reflected pressure varies with the angle of incidence of the shock wave and is typical maximal when shock wave impinges on a perpendicular surface (angle of incidence of 0°), is minimum when the surface is parallel (angle of incidence) 90° and has a maximum due to Mach reflections around 45°. The coefficient of reflection is typically 2-13.
An alternative approach to protect against blasts is to install suspended seats and energy absorbing materials.
Problems associated with known blast-protection element include a large impulse transmitted to the vehicle from a blast and large deformation of the blast-protection element by blasts. In addition, the known blasts shields do not optimally use the tensile strength of the material they are made of.